Time delay relay having ambient compensated thermally responsive actuating means



Sept. 7, 1965 Filed Feb. 11, 1963 J. O. MOORHEAD ETAL TIME DELAY RELAY HAVING AMBIENT COMPENSATED THERMALLY RESPONSIVE ACTUATING MEANS 2 Sheets-Sheet 2 inventors. John 0. Maarkead, rfaFnz .D, Gaadz'n,

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United States Patent 3,205,327 TIME DELAY RELAY HAVING AMBIENT COM- PENSATED THERMALLY RESPONS'IVE ACTU- ATING MEANS John 0. Moorhead and John D. Goodin, Lexington, Ky., assignors to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Feb. 11, 1963, Ser. No. 257,535 15 Claims. (Cl. 200-122) This invention relates to time delay relays and more particularly to thermal time delay relays.

The present invention, while having more general uses, is particularly useful in applications for controlling an auxiliary heater for a heat pump (e.g., a space heater) and as a time delay control for air conditioners or for compressors in refrigeration systems.

Among the several objects of this invention may be noted the provision of an improved thermal time delay relay adapted to control an electrical circuit; the provision of such an improved thermal relay which includes ambient compensated thermally responsive actuating means; the provision of a thermal relay of the class described which includes snap-acting switch means; and the provision of a time delay relay of the class described which is simple in construction, compact in form and economical to assemble and manufacture.

Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combination of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described and the scope of which will be indicated in the following claims.

In the accompanying drawings in which one of various possible embodiments of the invention is illustrated:

FIG. 1 is a top plan view of a switch according to the present invention;

FIG. 2 is an enlarged sectional view taken on line 22 of FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view taken on line 3-3 of FIG. 2;

FIG. 4 is a bottom plan view of the switch shown in FIG. 1; and

FIG. 5 is an exploded perspective view of part of the thermally responsive actuating mechanism of the switch shown in FIG. 1. 7

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

Dimensions of certain of the parts as shown in the drawings may have been modified and/or exaggerated for the purposes of clarity of illustration.

Referring now to FIGS. 2 and 4, there is shown a time delay thermal relay according to the present invention and generally indicated at numeral 10. Relay or switch 10 includes a housing 12 formed of a conventional electrically insulating material, such as a moldable phenolic resinous material. As best seen in FIG. 2, housing 12 includes a base 14 and a peripherally extending skirt portion 16 on one side thereof, defining a cavity 18 for reception therein of electrically conductive snap-acting switch means generally indicated at numeral 40. Housing 12 also includes a plurality of upstanding wall portions 20, 22, 24 and 26 on the other side of base 14 which define a cavity 30 for reception of thermally responsive actuator means generally indicated at 70 and which will be described in greater detail below. Cover members (not shown) may be connected to the housing 12 to close cavities 18 and 30 after assembly of switch 10 has been completed.

Snap-acting switch means Referring now to FIG. 4, snap-acting switch means 40 is received within housing cavity 18 and comprises an electrically conductive flexible blade 42 cantilever mounted adjacent one end 44 thereof, on base 14. End 44 is firmly clamped between, and secured to base 14 and an electrically conductive terminal 46 by means of a rivet 48 which also electrically connects blade 42 to terminal 46. The free end of blade 42 carries a pair of electrical contacts 50 and 52 on opposite sides thereof, as best seen in FIG. 2, for alternate engagement, respectively, with electrical contacts 54 and 56 which are respectively carried by electrical terminals 58 and 60. Housing 12 supports and mounts terminals 58 and 60 on opposite sides of blade 42 and in the path of movement thereof, as best seen in FIGS. 2 and 4. Contacts 50, 52, 54 and 56 are formed of a suitable electrical current-conducting material such as silver or the like. Blade 42 is formed of a suitable highly electrically conductive spring material such as, for example, a beryllium-copper alloy or a phosphor-bronze alloy.

To provide for snap-acting movement of the flexible blade 42 to actuate the contacts, a spring member 62 is provided which is flexed into a U-shaped form (as seen in FIG. 2), with one end thereof connected with the blade 42 adjacent the contact-carrying end thereof, and the other end of the spring member connected with a centrally located tongue 64 formed integrally with the blade 42 as by blanking out portions of the center of the blade. Tongue 64 extends from its integral connection with end 44 of the blade toward the free contactcarrying end of the blade. As best seen in FIGS. 2 and 4, tongue 64, adjacent its interconnection with spring 62, is provided with a dimpled or raised abutment portion 66 for engaging a motion transfer member to be described in greater detail below.

The tendency of the spring 62 to straighten out urges blade 42 either upwardly or downwardly as seen in FIG. 2, depending upon the position of tongue 64. Snapacting means 40 can be either of the so-called bistable or monostable types, depending uponp the spacing between the stationary contacts 54 and 56 relative to the neutral position of the blade 42, movement beyond which in either direction will cause snap-acting or over-centering movement. Switch means 40, as illustrated by way of example in FIG. 2,,is of the monostable type and contacts 52 and 56 are normally closed, so that upon removal of a force applied against tongue 64 to cause snap opening of contacts 52 and 56, blade 42 will automatically snap back to the FIG. 2 solid line position to reclose contacts 52 and 56.

Thermally responsive actuating means Switch 10 also includes a thermally responsive actuating means generally indicated at numeral 70 for causing snap action of means 40 to eifect contact actuation. Means 70 comprises two blade members 72 and 74, each of which are formed of a composite bimetallic thermally responsive material having a relatively high expansion component and a relatively low expansion component, as best seen in FIG. 2. Member 72, as best seen in FIGS. 1 and 5, is in the form of a frame and provides a substantially rectangular shaped window opening 76 which is defined by four legs 78, 80, 82 and 84. Member 72 can be formed from a sheet by a simple punching or blanking operation. Member 74 is substantially T-shaped and includes a transversely extending end portion 86. As best seen in FIGS. 2 and 5, end portion 86 and leg 84, respectively, of bimetal members 74 and 72 are arranged in stacked overlying relationship and mutually separated by a thermally and electrically insulating strip 90 formed,

80 of member 72.

for example, of mica. This stacked assembly is cantilever mounted on an extension92 of an electrically conductive terminal member 94 by means of a pair of rivets 96. A thermally and electrically insulating strip 98 (formed, for example, of mica) separates bimetal member 74 from terminal portion 92. Rivets 96 not only serve to firmly cantilever mount the bimetal blade-insulator assembly but also serve to electrically connect bimetal member 72 with terminal 94. A lost motion connection for the other ends of bimetal members or blades 72 and 74 is provided by a bifurcated portion on the other end of member 74 as defined by fingers 1G2, 104 and 106, which receive and sandwich therebetween, leg

This connection permits relative sliding movement between the free ends of members 72 and 74 in a direction along the plane of these members, to avoid creating undesirable stresses and also confines upward and downward movement (as seen in FIG. 2) of the free ends of these members to movement in unison. Leg 80 is provided with a dimpled port-ion 110 which is positioned to engage one end of a motion transfer pin 112 which is slidably received in an aperture 114 provided by base 14 of the housing 12. The other'end of pin 112 is positioned to engage the dimpled portion 66 on the central tongue 64 of the snap-acting'blade 40 to cause tongue 64 to move'in response to unitary movement of bimetal members 72 and 74 to effect snap-acting motion of blade 40.

In practice terminal 94 and bimetal blades 72 and 74 are made up as a separate subassembly which is thereafter mounted on the housing by means of a threaded fastener 100. The bimetal members 74 and 72 are arranged and constructed to provide for ambient compensation. In this regard the inside bimetal components of the blades as are nearest one another or those which face one another, have relatively similar coefiicients of thermal expansion, i.e., these components either both have relatively low coefiicients of thermal expansion or both have relatively high coeflicients of thermal expansion. It is preferred (but not essential) that blades 72 and 74 be formed of the same or similar bimetal material. It will be seen from the above that when blades 72 and 74 are subjected to a change in ambient temperature (e.g., an increase) that the blades will tend to flex or move in opposite directions against each other which opposing movement will effectively cancel each other out to thereby prevent or at least minimize movement of blades 72 and 74 as a unit in response to changes'in ambient temperature. Upon heating of member 74 to a temperature different from that of member 72, member 74 will exert a flexing force against member 72 which is greater than the opposing flexing force exerted by member 72 against member 74, which will cause the free ends of members 72 and 74 to move in unison either downwardly or upwardly depending on whether the inside components of the blades have relatively low or relatively high coefficients of thermal expansion. In the exemplary embodiment shown inthe drawings, the inside components of the blades have relatively low coefficients of thermal expansion so that upon suitable differential heating of member 74, downward movement (as seen in FIG. 2) in unison of the freeends of members 72 and 74 will take place.

Relay includes an electrical heater 120 in the form of wire having substantial electrical resistance and located in close thermal juxtaposition to the bimetal member 74, whichby way of example is shown in FIG. 1 as being wrapped around member 74 and electrically isolated therefrom by a layer of electrically insulating material 122, which may, for example, bemica. One end 124, of the heater, is electrically connected to an electrically conductive terminal 126 which is located intermediate upstanding portions 24 and 26 of housing 12 and secured to base 14 by means of rivet 127. The other end 128 of the heater is electrically connected to bimetal member 72 which in turn is electrically connected to terminal 94. It will be understood that heater 120 can be placed in close thermal juxtaposition to member 74 other than by being wrapped thereabout. Heater 120 may be mounted separately from but in good heat transfer relation to member 74 as, for example, on a separate cantilever mounted insulating member (not shown).

Operation of relay 10 is as follows: Contacts 52 and 56 are normally closed, as shown in the FIG. 2 solid line position of the parts. Upon a change in ambient temperature (e.g., an increase) bimetal blades 72 and 74 will tend to flex in directions opposite to each other to produce substantially equal opposing forces with the result that little or no motion of the bimetal members takes place. However, when heater 120 is electrically energized (by the circuit in which terminals 94 and 126 are connected), member 74 becomes heated to a temperature different from that of member 72. This results in a downward flexure force (as seen in FIG. 2) exerted by member 74 which is greater than the opposing upward fiexure force exerted by bimetal member 72 causing downward movement in unison of the free ends of members 74 and 72 from the solid line to the broken line position shown in FIG. 2. This causes mot-ion transfer member 112 to move downwardly (within opening 114) against the dimpled portion 66 of the tongue 64 to move the latter to the FIG. 2 dashed line position to cause over-centering or snap movement of the blade 42 from the FIG. 2 solid line contacts 52, 56 closed, and contacts 50, 54 open position to the FIG. 2 broken line contacts 52, 56 open and contacts 50, 54 closed position. Contacts 5t) and 54 will remain closed (in the FIG. 2 broken line position) as long as motion transfer pin 112 is maintained in the broken line position by the forces exerted against it by the bimetal blades 72 and 74. Upon sufficient diminishing of the current in the heater 120, or upon de-energization of the heater, bimetal member 74 will cool and the blades 72 and 74 return to the FIG. 2 solid line position, and blade 42 will automatically snap back to the solid line FIG. 2 position to reclose contacts 52 and 56.

The U-shaped portion of frame 72 defined by legs 78,

'80 and 82 which projects from the cantilever mounted end leg 84 advantageously is relatively thermally isolated from heater 129 by the spacing between legs 78 and 82 from blade 74 which is positioned therebetween in the window opening 76, as best seen in FIG. 1. By this arrangement, blade 72 does not become heated to any substantial extent by heater 120. Insulators and 93 further serve to minimize heat transfer between blades 72 and 74 and between heater and blade 72 so that the heat generated by heater 120 is directed primarily to the blade 74 to raise the temperature of the latter above that of the ambient compensating blade 72 to produce desired contact actuating motion of the free ends of these members. However, total thermal isolation between bimetal blade 72 and 74 is nOt desired because by allowing some heat to be conducted from blade 74 to blade 72, faster resetting of contacts 52, 56 can take place when the heater current is sulficiently diminished or removed. Locating member 74 in the window opening 78 intermediate legs 76 and 82 in addition to providing for a compact construction also permits a substantial portion of the length of blade member 74 to lie substantially in the same plane as or at least very close to the plane of legs 78 "and 82, which avoids or at least minimizes creation of undesirable stresses upon temperature change which might tend to twist or rotate the free end of :blade 72. This also simplifies the construction and assembly of parts, and provides for compact construction. If desired leg 84 of blade 72 and portion 86 of blade 74 can be omitted and the unjoined ends of legs 78, 82 and of blade 74 can be cantilever mounted in the same plane on terminal 94 so that a greater portion of member 74 will lie substantially in the same plane with legs 7 8 and 82 to further minimize creation of undesirable twisting stresses and moments at the free ends of these members 72 and 74, when the later flex in response to temperature change. It will be seen from the above that the present invention provides for a thermal time delay relay (the time delay resulting from the time interval required for transferring heat from heater 120 to blade 74 and raising its temperature sufliciently to overcome the opposing fiexure force of blade 72), which comprises a minimum number of parts and which can be quickly and economically manufactured and assembled.

In view of the above, it will be seen that the several objects of the invention are achieved, and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter cointained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense, and it is also intended that the appended claims shall cover all such equivalent variations as come within the true spirit and scope of the invention.

We claim:

1. An electrical switch comprising a base; contacts mounted on said base; a pair of composite thermostatic blades cantilever mounted adjacent one end thereof in overlying relationship on said base, lost motion means interconnecting the other ends thereof permitting relative sliding movement between said other ends and confining upward and downward movement of the said other ends to movement in unison, the inside components of each of the blades such as are nearest one another having similar coeflicients of thermal expansion, whereby movement of said blades in response to changes in ambient temperature will be minimized, and said switch including means for heating one of said blades to a temperature diilerent than that of the other of said blades whereby to cause said blades to move in unison in one direction to provide contact actuation motion for said contacts.

2. An electrical switch comprising a base; contacts mounted on said base; a pair of composite thermostatic bl-a des cantilever mounted adjacent one end thereof on said base, means interconnecting the other ends thereof permitting movement between said other ends in .a direction along a plane contiguous with the faces of the blades and limiting movement to movement in unison of said other ends in a direction generally perpendicular to said plane, said one end of said blades being adjacently located and a substantial portion of each of said blades lying substantially in the .said plane, the inside components of each of the blades such as are nearest one another having s1milar coefiicients of thermal expansion, whereby movement of said blades in response to changes in ambient temperature will be minimized, and said switch including means for heating one of said blades to a temperature different than that of the other of said blades whereby to cause said blades to move in unison in one direction to provide contact actuation motion for said contacts.

3. An electrical switch comprising a base; contacts mounted-on said base; first and second composite thermostatic blades cantilever mounted adjacent one end thereof on said base; said one end of each of said blades being adjacently located, lost motion means interconnecting the other ends thereof permitting relative sliding movement between said other ends and, in a direction generally perpendicular to said sliding movement, to movement in unison of the other ends; said first blade having a pair of spaced apart legs extending from the cantilever mounted end of said first blade toward said other end thereof; said second blade having a portion located intermediate and spaced from said pair of legs and extending from the cantilever mounted end of said second blade toward the other end thereof; the inside components of each of the blades such as are nearest one another having similar coeflicients of thermal expansion, whereby movement of said blades in response to changes in ambient temperature will be minimized, and said switch including means for heating said second blade to a temperature different than that of said first blade whereby to cause said blades to move in unison in one direction to provide contact actuation motion for said contacts.

4. An electrical switch comprising a base; contacts mounted on said base; first and second composite thermostatic blades cantilever mounted adjacent one end thereof on said base; said one end of each of said blades being adjacently located; said first blade having a U-shaped portion extending from the cantilever mounted end thereof,'

said U-shaped portion including a pair of spaced apart legs interconnected adjacent the ends thereof remote from said cantilever mounted end by a bight portion; said sec ond blade including a portion positioned intermediate and spaced from said pair of legs and extending from the cantilever mounted end of said second blade toward the bight portion of said first blade; lost motion means interconnecting the end of said second blade portion remote from the cantilever mounted end thereof, with said bight portion; :the inside components of each of the blades such as are nearest one another having similar coeflicients of thermal expansion, whereby movement of said blades in response to change-s in ambient temperature will be minimized, and said switch including means for heating said second blade to -a temperature different than that of said first blade whereby to cause said blades to move in unison in one direction to provide contact actuation motion for said contacts.

5. The switch as set forth in claim 4 and wherein the inside components of said blades have relatively high coefiicients of thermal expansion.

6. The switch as set forth in claim 4 and wherein the inside components of said blades have relatively low coefficients of thermal expansion.

7. The switch as set forth in claim 4 and wherein said heating means comprises an electrical heater in wire-like form wrapped around said second blade and electrical insulating means interposed between said second blade and said electrical heater.

8. An electrical switch comprising a base; contacts mounted on said base; first and second composite thermostatic blades cantilever mounted adjacent one end thereof on said base; said one end of each of said blades being adjacently located; said first blade having a U-shaped portion extending from the cantilever mounted end thereof, said U-shaped portion including a pair of spaced apart legs interconnected adjacent the ends thereof remote from said cantilever mounted end, by a bight portion; said sec-ond blade including a portion positioned intermediate and spaced from said pair of legs and extending from the cantilever mounted end of said second blade toward the bight portion of said first blade; the end of said second blade portion remote from the cantilever mounted end thereof having a bifurcated portion providing at least a pair of spaced fingers which receive said bight portion therebetween to provide .a lost motion interconnection between said second blade portion and said bight portion; the inside components of each of the blades such as are nearest one another having similar coefiicients of thermal expansion, whereby movement of said blades in response to changes in ambient temperature will be minimized, and said switch including means for heating said second blade to a temperature different than that of said first blade whereby to cause said blades to move in unison in one direction to provide contact actuation motion for said contacts.

9. The switch as set forth in claim 4 and wherein the plane of said second blade portion and that of said pair of spaced-apart legs lie in closely spaced relationship.

10. The switch as set forth in claim 4 and wherein a substantial portion of the length of said second blade portion lies substantially in the same plane as that of the plane of said pair of spaced-apart legs.

11. A snap-acting thermal time delay relay comprising a base formed of electrically insulating material; electrically conductive snap-acting switching means mounted on said base; said snap-acting means mounting an electrical contact for movement into and out of engagement with a second electrical contact mounted on said base; first and second composite thermostatic blades cantilever mounted adjacent one end thereof on said base; said one end of each of said blades being adjacently located; said first blade having a U-shaped portion'extending from the cantilever mounted end thereof, said U-shaped portion including a pair of spaced apart legs interconnected adjacent the ends thereof remote from said cantilever mounted end by a bight portion; said second blade including a portion positioned intermediate and spaced from said pair of legs and extending from the cantilever mounted end of said second blade toward the bight portion of said first blade; lost motion means interconnecting the end of said second blade portion remote from the cantilever mounted end thereof, with said bight portion; the inside components of each of the blades such as are nearest one another having similar coefficients of thermal expansion, whereby movement of said blades in response to changes in ambient temperature will be minimized, and said switch including electrical heater means disposed in intimate heat transfer relation with said second blade for heating said second blade to :a temperature different than that of said first blade whereby to cause said blades to move in unison in one direction; a motion transfer member supported on said base and positioned intermediate the lost motion interconnected ends of said blades and said snap-acting means whereby when said second blade is heated to a predetermined amount by said electrical heater said blades will move in unison relative to said motion transfer memher to cause snap actuation of said contacts.

12. An electrical switch comprising a base; a pair of electrical contacts supported on said base; means mounting one of said contacts for movement into and out of engagement with the other of said contacts; first and second composite thermostatic blades cantilever mounted adjacent one end thereof on said base; said one end of each of said blades being adjacently located; said first blade having a U-shaped portion extending from the cantilever mounted end thereof, said U-shaped portion including a pair of spaced apart legs interconnected adjacent the ends thereof remote from said cantilever mounted end by a bight portion; said second blade including a portion positioned intermediate and spaced from said pair of legs and extending from the cantilever mounted end of said second blade toward the bight portion of said first blade; lost motion means interconnecting the end of said second blade portion remote from the cantilever mounted end thereof, with said bight portion; the lost motion interconnected ends of said blades being associated with said movable contact for movement of the latter into and out of engagement with the other of said contacts in response to movement of said blades in unison; the inside components of each of the blades such as are nearest one another having similar coefiicients of thermal expansion, whereby movement of said blades in response to changes in ambient temperature will be minimized, and said switch including means for heating said second blade to a temperature different than that of said first blade whereby to cause said blades to move in unison in one direction.

13. A snap-acting thermal time delay relay comprising a base formed of electrically insulating material; an electrically conductive snapsacting switching device cantilever mounted adjacent one end thereof on one side of said base; a first electrically conductive terminal mounted on said base and electrically connected with said one end of said snap-acting device; said snap-acting device carrying an electrical contact adjacent the free end thereof for movement into and out of engagement with a second electrical contact carried by a second electrically conductive terminal mounted on said one side of said base; first and second composite thermostatic blades cantilever mounted adjacent one end thereof on the other side of said base; said one end of each of said blades being a-djacently located; said first blade having a U-shaped portion extending from the cantilever mounted end thereof, said U-shaped portion including a pair of spaced-apart legs interconnected adjacent the ends thereof remote from said cantilever mounted end by a bight portion; said second :blade including a portion positioned intermediate and spaced from said pair of legs and extending from the cantilever mounted end of said second blade toward the bight portion of said first blade; lost motion means interconnecting the end of said second blade portion remote from the cantilever mounted end thereof, with said bight portion; the inside components of each of the blades such as are nearest one another having similar coefficients of thermal expansion, whereby movement of said blades in response to changes in ambient temperature will be minimized, and

said switch including electrical heater means disposed in' intimate heat transfer relation with said second blade for heating said second blade to a temperature different than that of said first blade where-by to cause said blades to move in unison in one direction; said electrical heater means being electrically connected to a third electrically conductive terminal mounted on said base and also being electrically connected at another part thereof with a-fourth electrically conductive terminal mounted on said base; said base providing an aperture; a motion transfer member disposed in said aperture and positioned intermediate the lost motion interconnected ends of said blades and said snap-acting device whereby when said second blade is heated to a predetermined amount by said electrical heater said blades will move in unison relative to said motion transfer member to cause snap actuation of said contacts.

14. An electric switch comprising a base; contacts mounted on the base, first and second composite thermostatic blades cantilever mounted adjacent one end thereof on said base and facing each other; said one end of each of the blades being adjacently located; the first blade having a generally U-shaped portion extending from the cantilever'mounted end thereof and lying in a plane, the bight of the U-shaped portion being furthermost from the mounting, the second blade including a portion positioned intermediate and spaced from the legs of said U-shaped portion and extending from the cantilever mounted end of said second blade toward the bight of said U-shaped portion and lying at least partially within the plane of the first blade, lost motion means interconnecting the bight of the first blade to the end of the second blade remote from the cantilever mounting, the bimetal components of the blades which face one another having similar coefficents of thermal expansion, whereby movement of said blades in response to changes in ambient temperature will be minimized, and said switch including means for heating the second blade to a temperature different than that of said first blade whereby to causesaid blades to move in unison in one direction to provide contact actuation motion for said contacts.

15. -An electric switch comprising a base; contacts mounted on the base, first and second composite thermostatic blades cantilever mounted adjacent one end thereof on said base; said one end of each of said blades being adjacently located, the first blade having a U-shapedportion extending from the cantilever mounted end thereof, the bight of the U-shaped portion being furt-hermost-from the mounting, the second blade extending intermediate and spaced from the legs of the U-shaped portion ofthe first blade, and lost motion means interconnecting the other end of the second blade with the bight of the U-shaped portion of the first blade the components of each of the blades having coefiicients of thermal expansion where- 9 10 by upon a change in ambient temperature the tendency for References Cited by the Examiner movement of the first bladetin one directilon is 'oifset by the UNITED STATES PATENTS tendency for movement of the second bade in the opposite direction so that movement of the blades in response g fiq to changes in ambient temperature will be minimized, and 5 2658975 11/53 lgg said switch including means for heating the second blade 2:936:354 5/60 Greig to a temperature different than that of the first blade EIGN PATENTS whereby to cause said blades to move in unison in one direction to provide contact actuation motion for said 10 341,583 11/59 Switzerlandcontacts. BERNARD A. GILH-EANY, Primary Examiner. 

1. AN ELECTRICAL SWITCH COMPRISING A BASE; CONTACTS MOUNTED ON SAID BASE; A PAIR OF COMPOSITE THEREMOSTATIC BLADES CANTILEVER MOUNTED ADJACENT ONE END THEREOF IN OVERLYING RELATIONSHIP ON SAID BASE, LOST MOTION MEANS INTERCONNECTING THE OTHERENDS THEREOF PERMITTING RELATIVE SLIDING MOVEMENT BETWEEN SAID OTHER NDS AND CONFINING UPWARD AND DOWNWARD MOVEMENT OF THE SAID OTHER ENDS TO MOVEMENT IN UNISON, THE INSIDE COMPONENTS OF EACH OF THE BLADES SUCH AS ARE NEAREST ONE ANOTHER HAVING SIMILAR COEFFICIENTS OF THERMAL EXPANSION, WHEREBY MOVEMENT OF SAID BLADES IN RESPONSE TO CHANGES IN AMBIENT TEMPERATURE WILL BE MINIMIZED, AND SAID SWITCH INCLUDING MEANS FOR HEATING ONE OF SAID BLADES TO A TEMPERATURE DIFFERENT THAN THAT OF THE OTHER OF SAID BLADES WHEREBY TO CAUSE SAID BLADES TO MOVE IN UNISON IN ONE DIRECTION TO PROVIDE CONTACT ACTUATION MOTION FOR SAID CONTACTS. 